Abstract
AbstractIn this work, continuous conversion coatings on the surface of in situ TiB2 particulate reinforced A356 composite were formed successfully by cerium surface treatment for the first time. Scanning electron microscope (SEM) analysis showed that the conversion coatings were inhomogeneous and could be divided into two types of regions, namely, fine crack region and noncrack region. Many cerium‐rich nano‐nodules were uniformly distributed in the whole coatings. Energy dispersive spectroscopy (EDS) analysis testified that the crack coatings mainly covered the interdendritic sites occupied by TiB2 particulates and Si phases. X‐ray photoelectron spectroscopy (XPS) analysis indicated that the conversion coatings were composed of CeO2, Ce2O3, Ce(OH)4, Ce(OH)3, and a little amount of Al2O3. The electrochemical polarization tests showed that the cerium‐conversion treatment markedly improved the corrosion resistance of in situ TiB2p/A356 composite in chloride environment, and the protection degree of the coatings was superior to that of conventional chromate‐conversion coating. According to these results, the formation mechanism of cerium‐conversion coatings was discussed. Copyright © 2008 John Wiley & Sons, Ltd.
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